What are the available values for the ExecuteWhen field for a StateChange workflow?

The StateChange workflows we are creating via Visual Studios via the DynamicOps Cloud Development Kit are automatically being set to run PreActivityExecution is there any documentation on the available values for the ExecuteWhen field?

<?xml version="1.0" encoding="utf-8"?>

<!--

Autogenerated xml file created by the DynamicOps Cloud Development Kit (TM) Visual Studio Addin

The Workflow "Foo" will be executed when a Machine Transitions to the State(s) "BuildingMachine".

-->

<plugins xmlns="http://dynamicops.com/schemas/externalwf">

  <plugin fullName="DynamicOps.External.RepositoryWorkflows.InvokeRepositoryWorkflow" priority="1">

    <MasterWFStateCriteria>BuildingMachine</MasterWFStateCriteria>

    <MasterWFTypeFullNameCriteria>*</MasterWFTypeFullNameCriteria>

    <ExecuteWhen>PreActivityExecution</ExecuteWhen>

    <AssemblyPath>[ExternalWorkflowsDirectory]\DynamicOps.External.RepositoryWorkflows.dll</AssemblyPath>

    <AllPropertiesExist>

      <Property>Foo</Property>

    </AllPropertiesExist>

    <WorkflowArguments>

      <NameValue name="WorkflowName">Foo</NameValue>

      <NameValue name="WorkflowTimeout">01:00:00</NameValue>

      <NameValue name="FailureState">DeactivateMachine</NameValue>

    </WorkflowArguments>

  </plugin>

</plugins>